This invention relates to a tele-objective lens consisting of a front lens group having a positive refractive power and a rear lens group having a negative refractive power.
With the telephoto objective lens, it has been the general practice to move the lens as a whole to effect focusing. In U.S. Pat. No. 4,045,128, however, an inventive type of telephoto objective lens is disclosed wherein the provision for focusing is made at a sub-group thereof. The present invention is related to improvements in the objective system of the type described in U.S. Pat. No. 4,045,128.
The widely accepted design for tele-objective lens developed about 15 years ago was to construct the front lens group from only one positive and only one negative elements. Recently, the general trend is to make use of an additional positive lens element for the purpose of facilitating correction of aberrations.
Because of the relatively large dimensions of the lenses constituting the front lens group to those of lenses rearwardly subsequent thereto, however, increases in the number of lens elements lead to a rapid increase in the production cost, and to a corresponding increase in the weight of the complete objective so that it is inconvenient for a hand-held camera to employ such objective lens, as the so established camera is difficult to manage in performing photography.